Fire Frequency and the Spatial Age Mosaic of the Mixed-Wood Boreal Forest in Western Canada

Abstract

One approach to ecosystem management is to emulate the effects of natural disturbance in producing landscape patterns; this approach requires a spatial analysis of the pattern and an understanding of the processes producing the pattern. Forested landscapes exhibit mosaic patterns of both stand types and ages. This study investigates the spatial mosaic of stand ages produced by high‐intensity stand‐replacing fires in the mixed‐wood boreal forest of western Canada. A high‐resolution, accurately dated, time‐since‐fire map for a large (3461 km2) contiguous area is used to produce the landscape survivorship distribution in which both spatial and temporal changes in fire cycle are statistically tested. Spatial multivariate analysis of the time‐since‐fire map is also used to investigate the spatial assembly of the age mosaic. Significant changes in fire cycle can be explained by climatic change as well as land use change in the surrounding area. The shift from a short (15 yr) fire cycle to a longer (75 yr) cycle after 1890 in the northern half of the study area coincides with climatic change at the end of the Little Ice Age. In the southern half of the study area, the short fire cycle continues after 1890 due to the spread of human‐caused fires from the adjacent area which was settled and cleared for agriculture during the first half of the 20th century. Upon completion of settlement in 1945, the fire cycle becomes significantly longer due to the fragmentation of the once continuous forest that surrounded the study area and from which the majority of large fires propagated in the past. The different fire cycle histories of the two parts of the study area also explain the spatial mosaic pattern of stand ages, sizes, and shapes. The extended period of the short fire cycle through the first half of this century in the southern region results in it being dominated by younger, larger, oblong‐shaped polygons with irregular edges: characteristics that describe the shapes of large burns. The northern region has generally older and smaller, more circular, compact polygons that are the remnants of larger much earlier burns that have since been overburned. The polygons in the northern region are more similar in size and shape but less similar in age to adjacent polygons than are those in the southern region. Thus, this study shows how spatial heterogeneity in the landscape mosaic pattern can be characterized and related to the disturbance history of an area. Furthermore, it provides evidence of the impacts on the age mosaic due to forest fragmentation in surrounding areas.

Fire Regime in Marginal Jack Pine Populations at Their Southern Limit of Distribution, Riding Mountain National Park, Central Canada

“…The causes for these frequent fires can be traced in the local history and are similar to findings in other areas and parks along the southern edge of the boreal forest [10,11,18,25,26,86]. Conducting forest surveys from 1906 to 1908, Dickson [35] described the fires and resulting forests of the Riding Mountain Forest Reserve.…”

“…In central Canada, little research has been conducted with regards to disturbance dynamics in the boreal and mixedwood forests [25,26]. A study conducted in the boreal plains (e.g., DMPF) indicated the prevalence of stand-replacing fires associated with major drought periods and a lengthening of the fire cycle since pre-European Settlement [25].…”

Divergent temporal trends of net biomass change in western Canadian boreal forests

“…Between 1950 and 2009, mean annual temperature varied from −2.38°C to 4.08°C and mean annual precipitation from 365 to 1184 mm. The major stand-replacing natural disturbance in this area is wildfire, with return intervals varying from 15 to 90 years (Larsen, 1997;Weir, Johnson, & Miyanishi, 2000). A total of 2911 permanent sampling plots were established by the Alberta and Saskatchewan governments to monitor forest growth using stratified random sampling, mostly during the 1960s and 1970s.…”

The climate, the fuel and the land use: Long‐term regional variability of biomass burning in boreal forests

“…In accordance with other studies (Blarquez et al, 2015;Carcaillet, Bergman, Delorme, Hornberg, & Zackrisson, 2007;Marlon et al, 2013), our statistical analyses did not highlight a significant relationship between land use and BB in any of the northern boreal forests clusters. However, we did not rule out the potential influence of first American nations on local fire activity in North America before the European colonization and the impact of the first settlements since the 19th century Fastie, Lloyd, & Doak, 2002;Natcher et al, 2007;Weir, Johnson, & Miyanishi, 2000), as well as the anthropogenic use of fire between the 18th and the 20th centuries in northern Fennoscandia (Aakala et al, 2018;Granström & Niklasson, 2008;Segertröm, Bradshaw, Hörnberg, & Bohlin, 1994;Zackrisson, 1977).…”